Directions: Find the wrong number in the series. 1, 3, 10, 21, 64, 129, 356, 777

### Concept & Logic Identify the pattern governing the transition between consecutive terms in the series. ### Step-by-Step Solution 1. Let's analyze the relation between consecutive terms. 2. $1 \times 2 + 1 = 3$ 3. $3 \times 3 + 1 = 10$ 4. $10 \times 2 + 1 = 21$ 5. $21 \times 3 + 1 = 64$ 6. $64 \times 2 + 1 = 129$ 7. $129 \times 3 + 1 = 388$ (Wait, the given term is $356$) 8. Let's check the next term with $388$: $388 \times 2 + 1 = 777$. This matches the last term. 9. So, the pattern is alternate multiplication by $2$ and $3$, followed by adding $1$. 10. The incorrect term is $356$; it should be $388$. ### Exam Strategy & Shortcut When you see numbers growing rapidly but inconsistently, look for alternating patterns or combinations of multiplication and addition. ### Common Pitfall Assuming a single simple operation (like constant addition) instead of checking for alternating multiplicative patterns. ### Final Answer Therefore, the correct answer is **356**.